To Topical dosage forms have been widely prescribed for decades in the treatment of systemic diseases and local conditions such as those involved with the skin and underlying tissues. Certain drugs are relatively easy to be delivered via the transdermal or transmucosal route because they can easily permeate through the skin or mucosal membrane at a high potency. Permeation of the drug across the skin or mucosal membrane from a transdermal patch or a mucosal patch is a result of the chemical potential gradient across the skin or mucosal membrane. Examples of these drugs include nitroglycerin, scopolamine, nicotine, hydrocortisone, betamethasone, benzocaine, and lidocaine.
Most drugs and biological active ingredients, however, cannot readily penetrate through the skin or mucosal membrane. Therefore, to increase skin permeation of these drugs, various chemical and physical permeation enhancing methods have been employed. Chemical permeation enhancing agents may be applied typically to increase transdermal delivery of drugs. Generally, chemical permeation enhancing agents are cost effective and safe. An extensive review of chemical penetration enhancing agents is reported in Buyuktimkin et al., “Chemical Means of Transdermal Drug Permeation Enhancement”, Transdermal and Topical Drug Delivery Systems, Interpharm Press, Inc., 1997, pages 357-475. One major disadvantage associated with chemical penetration enhancers is potential skin irritation.
Physical penetration enhancing methods can also be used to improve transdermal drug delivery. The energy forms employed for this purpose include electricity (e.g., iontophoresis), ultrasound (e.g., phonophoresis) and thermal energy (e.g., heat-assisted delivery), which are reviewed by Sun, “Skin Absorption Enhancement by Physical Means: Heat, Ultrasound, and Electricity”, Transdennal and Topical Drug Delivery Systems, Interpharm Press, Inc., 1997, pages 327-355.
U.S. Pat. No. 4,898,592 relates to a device for the application of heated transdermally absorbable active substances that includes a carrier impregnated with the transdermally absorbable active substance and a support. The support is a laminate made up of one or more polymeric layers and optionally includes a heat conductive element. This heat conductive element is used for distribution of the patient's body heat such that absorption of the active substance is enhanced. This device, however, has no heat-generating element or function. The use of only a heat conductive element to distribute body heat, however, is not an efficient or reliable method of enhancing transdermal absorption by heating since the amount of body heat given off by a patient can vary depending on the ambient air temperature and the physical conditions of the patient.
U.S. Pat. No. 4,747,841 discloses a method and apparatus for “moxibustion” using a heat-generating element to heat and vaporize “moxall ” for treatment of a patient's skin without leaving burn scars. The objective of this method and apparatus, however, is to achieve heat stimulation of the body and not to increase skin permeability.
U.S. Pat. No. 4,230,105 discloses a bandage with a drug and a heat-generating substance, preferably intermixed, to enhance the rate of absorption of the drug by the user's skin. Separate drug and heat-generating generation substance layers are also disclosed. water must be applied to the bandage to activate the heating substance to release solvation heat. Because the exothermal reaction during the hydration of the electrolytes disclosed in this patent only produces a transient low level of heat, it cannot be effectively used as a penetration enhancing method over a long period of time (e.g., for up to one day). Further, the speed of the hydration process is rather difficult to control.
U.S. Pat. No. 4,685,911 discloses a skin patch including a drug component and an optional heating element for melting the drug-containing formulation if the user's body temperature is inadequate to do so. The heating element is not substantially co-extensive with the drug reservoir, the latter being quite thick and, thus, not susceptible to even and rapid onset of heating. There is also no description on how to control the exothermic reaction to have prolonged and even heating.
U.S. Pat. No. 4,963,360 describes an exothermic device having a carrier layer, which comprises a medicinal component, and an exothermic layer, which develops heat when exposed to the air to enhance absorption of the medicinal component through the skin. The exothermic layer comprises a mixture of iron powder, carbon powder, salts (i.e., sodium chloride and aluminum chloride), and water. There is a base sheet to separate the exothermic layer from the medicinal layer in two separate chambers, and an air-permeable film that covers the exothermic layer.
U.S. Pat. No. 5,658,583 describes a heat-generating generation apparatus for improved dermal permeation of pharmaceuticals. The apparatus includes a thin drug formulation reservoir and a heat-generating chamber separated by a non-permeable wall. The drug formulation reservoir houses a predetermined amount of a formulation containing pharmaceutical agents. The heat-generating/temperature-regulating chamber includes a heat-generating medium consisting of carbon, iron, water and/or salt which is activated upon contact with oxygen in the air. The structure of the apparatus also includes a cover that is not permeable to air, but is perforated with holes to regulate the contact between the heat-generating medium and air, thereby, controlling the heating temperature.
U.S. Pat. No. 5,662,624 describes a heat dressing for treatment of skin areas comprising a heat generating unit and a liquid-absorbing adhesive layer that, prior to use, is coated with a release layer. The adhesive layer is preferably made of a hydro-colloidal material and may optionally contain one or more medicaments or may be coated with alginate fiber mats. The heat-generating unit generates heat preferably by means of galvanic or chemical energy, and the heat dressing may further comprise elements for controlling the heat development and/or the surface temperature. Such elements include a cover sheet for the heat-generating unit that is perforated for air passage, is covered by a heat-reflecting foil, or is a polymeric foam to better retain the heat.
The present invention relates to an exothermic delivery device for administration of active agents through a barrier membrane (e.g., the skin, mucosal membrane, or nails of a human). The advantages of the present device include: better-controlled heatgeneration process, and consequently, an improved delivery profile of the active agents; an easier control on the product stability during storage; and simple manufacturing process for the device.